An initial attempt at a CONTRIBUTING document

This CONTRIBUTING document can help describe our development
workflow to anyone submitting changes to the project.

I've gone with a basic description of our new branching system and
some getting started links for creating patches through forking
and branching. It's probably best to lean toward a trim page here,
but it is nice to have as much relevant information as possible.
Update formatting around commit example
Commits section doesn't need to be an ordered list

Because formatting. :)
Merge pull request #127 from washingtonstateuniversity/contributing

[PR] An initial attempt at a CONTRIBUTING document